In order to provide versatility to the equipment in thermoforming shallow items such as lids for containers and the like from both oriented and non-oriented thermoplastic materials of the solid (as opposed to foamed) type, orientation of such materials ordinarily requires temperatures to be lower than those for non-oriented materials in order to achieve proper retention of orientation in the finished product. Certain materials at these lower temperatures are more difficult to thermoform and provide the desired ultimate detail with only vacuum pressure behind the thermoforming draw. Accordingly, additional pressure or pressure assist is needed in order to enhance the detail in the finished product. This is provided by placing positive pressure on one side of the web being thermoformed with or without vacuum on the other.
In the prior art, this additional pressure was achieved by a clamshell type device consisting of a lid at one edge of the mold pivoted from a position across the mold face to a position 90.degree. from the mold face to permit insertion and ejection of thermoformable web and finished product, respectively. However, because of the inertias involved in operating such a trap door or clamshell type pressure lid over a mold cavity, this system becomes very cumbersome at high speeds. The present invention is directed to pressure assist devices synchronized with rotary molding devices such that high speeds are achievable without the sacrifice of quality.
Continuous rotary in-line thermoforming devices operating at relatively high speeds of the plug assisted or match molding type require accurate indexing of the plug devices or male match molding devices with the mold cavities in a rotary mold wheel while at the same time keeping inertial changes to an optimal minimum.
It is an object of the present invention to provide continuous rotary in-line thermoforming systems and methods in which pressure, plug assist and match mold devices are accurately indexed at high speeds with the rotary mold means and mold cavities therein.
Another object of the present invention is to provide new and novel pressure assist means for rotary in-line thermoforming systems.
Still another object of this invention is to provide new and novel plug assist means and indexing and drive means for same for continuous rotary in-line thermoforming systems.
Yet another object of the present invention is to provide new and novel match mold means and indexing and drive means for same for continuous in-line rotary thermoforming systems.
These and other objects of the present invention will become more fully apparent with reference to the following specification and drawings which relate to several preferred embodiments of the present invention.